**Cylindrical capacitors:-**

Unlike plate capacitors where 2 plates are used to
form a capacitor, cylindrical capacitors are made by using two concentric
cylindrical shells or wires and these two cylinders and wires are separated by
using a dielectric medium.

Only
difference between plate capacitor and cylindrical capacitor is its shape.

Electrical
cable is best example for cylindrical capacitors.

**How to calculate capacitance of a Cylindrical capacitor:-**

For
Calculating capacitance of a cylindrical capacitor let’s take radius of inner
cylinder as r1 and outer cylinder as r2. Now let’s take permittivity of dielectric
material used to form capacitor as εa.

As
in case of plate capacitor where one plate is acts cathode and other acts as an
anode now in similar case let’s take inner cylinder charge per meter length on
outer surface of inner cylinder as +q and similarly on inner surface of outer
cylinder as –q coulombs.

In
practical +q charge is considered to be on axis and outer circle is earthed so
that person touching the capacitor doesn’t get the shock.

Now
for calculating capacitance of capacitor:-

Surface
area of the coaxial cylinder = 2

x=
Radius of cylinder a meter and

Length
=1 meter

Now
electrical field intensity at “x” meter away from center of inner cylinder is
as below:-

Ex =

__Q__Volt/Meter
2πεoεax

Where
εo= Permittivity of vacuum or
permittivity of free space, its value is 8.84 x 10

^{-12 }Farad/meter
Potential
difference between two plates or two cylinders is as below:-

So
more will be the length of capacitor more will be the capacitance.

Capacitor
is also known as condenser.